package org.apache.lucene.store;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import org.apache.lucene.util.ThreadInterruptedException;
import java.io.IOException;

/** An interprocess mutex lock.
 * <p>Typical use might look like:<pre>
 * new Lock.With(directory.makeLock("my.lock")) {
 *     public Object doBody() {
 *       <i>... code to execute while locked ...</i>
 *     }
 *   }.run();
 * </pre>
 *
 * @see Directory#makeLock(String)
 */
public abstract class Lock {

    /** How long {@link #obtain(long)} waits, in milliseconds,
     *  in between attempts to acquire the lock. */
    public static long LOCK_POLL_INTERVAL = 1000;

    /** Pass this value to {@link #obtain(long)} to try
     *  forever to obtain the lock. */
    public static final long LOCK_OBTAIN_WAIT_FOREVER = -1;

    /** Attempts to obtain exclusive access and immediately return
     *  upon success or failure.
     * @return true iff exclusive access is obtained
     */
    public abstract boolean obtain() throws IOException;

    /**
     * If a lock obtain called, this failureReason may be set
     * with the "root cause" Exception as to why the lock was
     * not obtained.
     */
    protected Throwable failureReason;

    /** Attempts to obtain an exclusive lock within amount of
     *  time given. Polls once per {@link #LOCK_POLL_INTERVAL}
     *  (currently 1000) milliseconds until lockWaitTimeout is
     *  passed.
     * @param lockWaitTimeout length of time to wait in
     *        milliseconds or {@link
     *        #LOCK_OBTAIN_WAIT_FOREVER} to retry forever
     * @return true if lock was obtained
     * @throws LockObtainFailedException if lock wait times out
     * @throws IllegalArgumentException if lockWaitTimeout is
     *         out of bounds
     * @throws IOException if obtain() throws IOException
     */
    public boolean obtain(long lockWaitTimeout) throws LockObtainFailedException, IOException {
        failureReason = null;
        boolean locked = obtain();
        if (lockWaitTimeout < 0 && lockWaitTimeout != LOCK_OBTAIN_WAIT_FOREVER)
            throw new IllegalArgumentException("lockWaitTimeout should be LOCK_OBTAIN_WAIT_FOREVER or a non-negative number (got " + lockWaitTimeout + ")");

        long maxSleepCount = lockWaitTimeout / LOCK_POLL_INTERVAL;
        long sleepCount = 0;
        while (!locked) {
            if (lockWaitTimeout != LOCK_OBTAIN_WAIT_FOREVER && sleepCount++ >= maxSleepCount) {
                String reason = "Lock obtain timed out: " + this.toString();
                if (failureReason != null) {
                    reason += ": " + failureReason;
                }
                LockObtainFailedException e = new LockObtainFailedException(reason);
                if (failureReason != null) {
                    e.initCause(failureReason);
                }
                throw e;
            }
            try {
                Thread.sleep(LOCK_POLL_INTERVAL);
            } catch (InterruptedException ie) {
                throw new ThreadInterruptedException(ie);
            }
            locked = obtain();
        }
        return locked;
    }

    /** Releases exclusive access. */
    public abstract void release() throws IOException;

    /** Returns true if the resource is currently locked.  Note that one must
     * still call {@link #obtain()} before using the resource. */
    public abstract boolean isLocked() throws IOException;

    /** Utility class for executing code with exclusive access. */
    public abstract static class With {
        private Lock lock;
        private long lockWaitTimeout;

        /** Constructs an executor that will grab the named lock. */
        public With(Lock lock, long lockWaitTimeout) {
            this.lock = lock;
            this.lockWaitTimeout = lockWaitTimeout;
        }

        /** Code to execute with exclusive access. */
        protected abstract Object doBody() throws IOException;

        /** Calls {@link #doBody} while <i>lock</i> is obtained.  Blocks if lock
         * cannot be obtained immediately.  Retries to obtain lock once per second
         * until it is obtained, or until it has tried ten times. Lock is released when
         * {@link #doBody} exits.
         * @throws LockObtainFailedException if lock could not
         * be obtained
         * @throws IOException if {@link Lock#obtain} throws IOException
         */
        public Object run() throws LockObtainFailedException, IOException {
            boolean locked = false;
            try {
                locked = lock.obtain(lockWaitTimeout);
                return doBody();
            } finally {
                if (locked)
                    lock.release();
            }
        }
    }

}
